1. Field of the Invention:
The present invention relates to a steering system for front and rear wheels of a motor vehicle wherein the steering ratio of the rear wheels to the front wheels is variable dependent on the speed of the motor vehicle.
2. Description of the Prior Art:
There has been proposed a steering system for front and rear wheels of a motor vehicle (Japanese Patent Application No. 56-134888 filed on Aug. 2, 1982 and laid-open on Feb. 10, 1984 under JP-A-59-26363). According to the proposed steering system, a front wheel steering mechanism and a rear wheel steering mechanism are operatively interconnected, and the steering ratio of the rear wheels to the front wheels is variable dependent on the speed of the motor vehicle. More specifically the rear wheels are steered in opposite phase with the front wheels, or substantially not steered at lower vehicle speeds, and the rear wheels are steered in phase with the front wheels at higher vehicle speeds.
When the motor vehicle is decelerated while the steering angle is kept constant at the time the motor vehicle is turned with the rear and front wheels steered in phase at a higher vehicle speed, the proposed steering system causes the steering angle of the rear wheels to be reduced, that is, the steering system causes the difference between steering angles of the front and rear wheels to vary, with the result that the radius of turning movement of the motor vehicle varies. Conversely, when the vehicle speed is increased at a constant steering angle, the radius of turning movement of the vehicle is increased, that is, understeer results.
Many ordinary motor vehicles in which the rear wheels are not steerable are designed to exhibit understeer for stability during high-speed travel of the motor vehicle. When the motor vehicle with an understeering tendency is decelerated, the radius of a turn is also reduced. However, the motor vehicle equipped with the system for varying the steering ratio of the rear wheels to the front wheels dependent on the vehicle speed tends to understeer at a greater rate than the ordinary motor vehicles.
Therefore, the driver of a motor vehicle with such a variable steering ratio is required to perform a greater compensatory operation of the steering wheel for an increase or reduction in the vehicle speed than would be required with a motor vehicle of ordinary construction having unsteerable rear wheels.